United States Office of Water EPA-822-F-01-010 

Environmental Protection 4304 December 2001

Agency

 

FACT SHEET

 ECOREGIONAL NUTRIENT CRITERIA

Summary

The U.S. Environmental Protection Agency (EPA) is publishing nine new nutrient water quality

criteria documents for lakes and reservoirs, and rivers and streams within specific geographic

regions (ecoregions) of the United States. These recommended section 304(a) water quality

criteria for nutrients were developed with the aim of reducing and preventing eutrophication on a

national scale. Each document presents recommended criteria for causal parameters (total

phosphorus and total nitrogen) and response variables (chlorophyll a and some form of water

clarity, i.e., turbidity or Secchi depth). This information is intended as a starting point for states,

authorized tribes and others to develop more refined nutrient criteria, as appropriate, using EPA

waterbody–specific technical guidance manuals and other scientifically defensible approaches. 

EPA will work with states and authorized tribes as they adopt water quality criteria for nutrients into

their water quality standards. 

Background

EPA is publishing nine new ecoregional

nutrient criteria documents to support the

development of state and tribal nutrient

criteria for two waterbody types - lakes and

reservoirs, and rivers and streams. These

nine documents cover four nutrient

ecoregions for lakes and reservoirs and five

nutrient ecoregions for rivers and streams.

They collectively present approximately

160 individual water quality criteria for

nutrients. (There are a total of fourteen

nutrient ecoregions.) EPA issued

seventeen ecoregional nutrient criteria in

January 2000. EPA’s nutrient website

(www.epa.gov/ost/standards/nutrient.html)

 presents the geographic coverage 

and the recommended nutrient water

quality criteria for each nutrient ecoregion.

Why is EPA publishing Ecoregional

Nutrient Criteria? 

The national goals of the Clean Water Act

are to achieve, wherever attainable, water

quality which provides for the protection

and propagation of fish, shellfish, and

wildlife and recreation in and on the water. 

As part of state and tribal water quality

standards, the Clean Water Act requires

states and authorized tribes to specify

designated uses for their waters in

consideration of the these goals, and to adopt

water quality criteria that protect those

designated uses. To help states and tribes,

EPA develops and publishes national criteria

guidance and information. This information

presents the latest scientific knowledge on the

effects of pollutants on biological community

diversity, productivity, and stability, including

information on the factors affecting rates of

eutrophication (excess amounts of nutrients

that stimulate undesirable plant growth) for

receiving waters.

Overview of the Problem

Eutrophication of United States surface waters

is a long standing problem. As much as half of

the Nation’s waters surveyed by states and

tribes do not adequately support aquatic life

because of excess nutrients. Nitrogen and

phosphorus are the primary causes of

eutrophication and resulting algal blooms. 

Chronic symptoms of overenrichment include

low dissolved oxygen, fish kills, cloudy murky

water, and depletion of desirable flora and

fauna. Nutrient levels that lead to these

problems vary from one region of the country to

another due to geographical variations in

geology, climate and soil types. In order to be

most effective, therefore, state and tribal water

quality criteria need to take into account

ecoregional variations.
What are ecoregional nutrient criteria

and how should they be used?

Nutrient criteria are numerical values for

both causative (phosphorus and nitrogen)

and response (chlorophyll a and turbidity)

variables associated with the prevention

and assessment of eutrophic conditions. 

EPA’s recommended ecoregional nutrient

criteria represent conditions of surface

waters that have minimal impacts caused

by human activities. Therefore, when a

state or tribe applies these criteria, the

waters are protected from the harmful

consequences of nutrient overenrichment.

These recommended water quality criteria

are suggested baselines which states and

tribes should refine to help identify problem

areas, serve as a basis for state and tribal

water quality criteria for nutrients, and

evaluate relative success in reducing

eutrophication. 

What are the activities

related to these criteria documents?

EPA published a Notice of Availability in the

Federal Register to solicit scientific views

on the criteria documents. EPA will review

and consider new information submitted by

the public on significant scientific issues

and site-specific data. EPA will also forward

pertinent data submitted by the public to

the appropriate Region to help develop

more refined local criteria.

The criteria have been through external

peer review, and a summary of these

comments are available on the Nutrient

website

(www.epa.gov/ost/standards/nutrient.html) 

EPA intends to complete publication of 

ecoregional nutrient criteria documents for

lakes and reservoirs, rivers and streams,

and wetlands within the remaining

ecoregions, as well as estuarine and

coastal waters in the near future.

What are EPA’s expectations for these

criteria? 

EPA expects that states and tribes will use

these nine ecoregional nutrient criteria

documents as starting points to identify

more precise numeric levels for nutrient

parameters needed to protect aquatic life,

recreational, or other uses on site-specific

or subregion-specific conditions. EPA expects

these more precise numerical levels to be

developed on a smaller geographic scale than

the ecoregional values presented in the nutrient

water quality criteria documents. States and

tribes may also develop criteria using other

scientifically defensible methods and

appropriate water quality data or simply adopt

EPA’s recommended water quality criteria in

their water quality standards. EPA expects

states and tribes to prepare a plan for adopting

nutrient criteria and to adopt new or revised

nutrient criteria into their water quality

standards.

Will these criteria be revised in the future?

After we review the submitted significant

scientific information, EPA may publish either

revised criteria or a notice informing the public

that it does not intend to revise the documents

presently. EPA will, however, update the

criteria as new scientific information becomes

available. 

How do I obtain a copy of the documents?

You can get copies of the complete set of nine

ecoregional criteria documents, or a specific

ecoregional criteria document from EPA’s

National Service Center for Environmental

Publications (NSCEP), 11029 Kenwood Road,

Cincinnati, OH 45242; (513) 489-8190 or toll

free (800) 490-9198. You can also get copies

by contacting the Water Resource Center at

(202) 260-7786. Alternatively, consult EPA’s

nutrient website at

www.epa.gov/ost/standards/nutrient.html for

downloads. EPA’s waterbody-specific technical

guidance manuals, which present the Agency’s

recommended nutrient criteria derivation

methodology, are also available at this website.